Re: What's the connection between objects and threads?
On May 19, 12:58 am, Ian Collins <ian-n...@hotmail.com> wrote:
Gianni Mariani wrote:
Ian Collins wrote:
....
You still have not addressed the fundamental issue of the
new thread using an object that has not been fully
constructed. Please provide example code that solves this
problem.
Almost all threaded code I have seen that works in a cross
platform is susceptible to the "problem" in a strict sense.
In practice, if the thread is "enabled" as the very last
thing in the most derived constructor, then there it is very
unlikely you're ever going to see a problem.
The problem is the thread class tends to be used as a base, so
this strict rule breaks down.
I have yet to find an alternative that is acceptably
straight forward as this approach.
I guess I was bitten by it too often in my formative years and
moved to the functor style now adopted by boost. Now I find
the boost style much more straight forward and less fragile.
The object used for the thread is always complete and in a
known state.
That is, IMHO, the cleanest solution. When it comes down to
it, the "object" you execute on isn't the thread; it's used by
the thread, so even from an OO point of view, it seems
preferable.
The alternative is to provide a separate function to start the
thread, as in Java. I personally don't see where this is a
problem either; it's just one additional function call after the
constructor. If the execution object has significant behavior,
it might even be preferable; it gives you a chance to intervene
after the constructor, but before the thread starts (e.g. to
register the object somewhere).
All in all, I don't really believe in the one size fits all
philosophy here, but if I had to stick to just one model, it
would be that of Boost, which executes a copy of the object you
pass it. It's a slight hassle in the case of joinable threads,
if you want to access the results in the thread object after the
join, but that's nothing that an extra layer of indirection
can't fix. (Back in the old days, it was widely believed that
there was no problem which couldn't be solved by an extra layer
of indirection:-).) (What bothers me most about the Boost model
is that if you miss catching an exception somewhere, you end up
with a detached thread, when what you wanted was to terminate
and join.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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